1. Field of the Invention
The present invention relates to decoy projectiles which can be fired into the air and which, after igniting, will emit infrared radiation so as to divert incoming missiles having infrared search heads from their path of travel and away from their intended targets.
2. The Prior Art
Infrared radiation-emitting decoy projectiles are known. These projectiles are, for example, carried on ships so that when the ship's detection instruments detect the approach of an incoming missile equipped with an infrared search head, the projectile can be fired into the air and subsequently, i.e., at a predetermined height and distance from the ship, it will ignite and eject combustible flakes which burn and emit infrared radiation. These combustible flakes will actually form a burning interference cloud which will descend slowly toward the earth and divert the approaching missile(s) toward itself and away from the ship. A projectile of this type is, for example, disclosed in German Pat. No. 28 11 016.
Comprehensive studies have now shown that the infrared radiation of such an interference cloud exhibits a very characteristic radiation emission sequence. Ignition of the igniter-destructor charge in the projectile first results in a "radiation flash," which is radiation of high intensity but which lasts an extremely short time, after which the radiation from the combustible flakes is emitted in such a way that at first there occurs a more or less steep increase in radiation (ignition phase of the combustible flakes) up to a certain maximum (all flakes are burning over their entire surface), followed by constant or insignificantly declining radiation, and then by a more or less sudden decrease of the trailing wave front, i.e., as the combustible flakes stop burning. Between the initial radiation flash and the point at which the combustible flakes emit maximum radiation, there is consequently a "radiation gap" whose duration depends on the steepness of the wave front of the radiation from the combustible flakes. As such, the "radiation gap" is determined by the reaction velocity of the combustible layer of combustible flakes.
Additional studies have now been carried out to ascertain whether and in what way the noted radiation gap can effect the protection offered by the interference cloud. It has been shown that this effect can generally be disregarded when the protection of a medium-sized and medium-fast target is involved, for instance, a torpedo patrol boat. Projectiles for boats of this class are equipped with combustible flakes having a burning time of 10 to 20 seconds, which means a relatively fast-reacting combustible layer and a relatively short radiation gap; moreover, such boats, because of their maneuverability, are protectable by quick, evasive action.
However, when protection of very rapidly moving targets is involved, particularly airplanes, the above-mentioned radiation gap can lead to diminished protection since the distance between the airplane and the radiation cloud increases very rapidly. Although it is possible to overcome this problem by reducing the radiation gap, i.e., by increasing the reaction velocity of the combustible layer of combustible flakes such that its burning period is about five seconds, actual results obtained have not been entirely satisfactory, particularly since, as a result of the high speed of movement of the combustible flakes in relation to the air, even with fast reacting combustible layers there is a delay in the ignition process.
On the other hand, the above-mentioned radiation gap has a negative effect on the protection of very large, slow-moving targets, such as ships of considerable size, although for a very different reason from that of the previously mentioned situation with airplanes. To protect large ships, very early recognition of the approaching missile is necessary, not only because of the low maneuverability of such ships but also because the incoming missile can only be deviated from its course if both the ship and the nearby interference cloud appear in its search field, which is only possible when the missile is still far away from the ship. The requirement of a comparatively early formation of the radiation cloud also means that the radiation time of the cloud must be quite extensive; thus the combustible flakes must, for instance, burn for 30 to 40 seconds. This is only possible when the reaction velocity of the combustible layer is very slow, resulting in a very slow burning process. This leads to such a prolongation of the radiation gap that the timely diversion of the missile can no longer be assured when immediate measures are required, i.e., when the approaching missile is very close to its target when detected. This disadvantage in terms of immediate counter-measures is independent of the size and speed of the target to be protected.
It is, therefore, the object of the present invention to provide an improved infrared radiation-emitting projectile wherein the described radiation gap of the forming radiation cloud is considerably reduced, regardless of whether the combustible layers in the projectile have short, long or very long burning periods.